Telephone system



June 23, Q E. LOMAX y TELEPHONE SYSTEM Filed April 22, 1940 3 Shee'fs-Sheet l mbv R B3. KEW @j m mbv@ @FLUQQQ 2.35m m #SEG m Y Lokumwq al Om, WND E QN l IV Al Iv Y SN WQ QN QN @Q\\ .Ml Q35@ Q25@ #SEG NN #3.2.5 Qtto Lw E UEJ- m25 Jmo N D M m23 m03 WN SQ LOWQQQQ SEEK NNN Clarence Ernest Lomax BY MIM, M M

ATTORNEYS June 23, 1942. c. E. LOMAX TELEPHONEi SYSTEM 3 Sheets-Sheet 2 Filed April 22, 1940 9W QUESM w00 mtrmxmmw INVENTOR Clarence Ernesz Lamai:v

A I B Y A M ATTORNEYS `lune 23, 1942. c. E. LOMAX y v TELEPHONE SYSTEM Filed April 22,' 1940 3 Sheets-Sheet 3 *tmmb mtas@ Opm, QDM

25ms @SU WII N mm Mmmm .mmm .1@ www QQNSQAG MES llNyEN-ron Ernes Lomax Patented June 23, 1942 TELEPHONE SYSTEM Clarence Ernest Lomax, Oak Park, Ill., assigner to Associated` Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application April 22, 1940, Serial No. 330,977

se claims.v (ol. 1ro- 27) The present invention relates to telephone systems and more particularly to improved apparatus for setting up reverting call connections between two substations associated with the same multiparty subscribers line- In existing telephone installations no provisions are made for informing the recipient of a reverting call as to the type of call being answered. More particularly, two methods of han* dling reverting calls are extensively used, in sys tems of the automatic type. According to'l one of these methods, commonly known as the directory number dialing method, the calling subscriber, after dialing the directory number of the called substation, restores his receiver to its supporting hoc-k or cradle, and after waiting a reasonable time interval again removes his receiver from its supporting hook or cradle to prepare or complete the desired connection, depending upon whether the call has been answered at the called substation. If, during this interval, the call is answered at the called substation, the answering party receives the impression of a dead line, due to the fact that he receives no response to his answering salutation, The-other method commonly used in handling reverting calls in automatic systems is that of providing reverting call switches for selective ringing purposes. In practicing this method the substation associated with the multiparty subscribers lines are provided with special directory number listings. These special directory numbers must be dialed by calling subscribers in order to set up reverting call connections. This method is also open to the objection that a party answering a reverting call is not informed as to the character of the call and, accordingly, may assume that the call has 'been abandoned. The method of procedure followed in manual systems in handling reverting calls is also open to the disadvantage brieliy outlined above.

It is an object of the present invention, therefore, to provide improved apparatus for' setting up reverting call connections between the substaticns associated with the multiparty lines of a telephone system, which is so arranged that the character of reverting calls is indicated to the parties answeringfsuch calls.

It is another object ofthe invention to provide for use in an'automatic telephone system an improved reverting call signaling arrangement which is equipped to transmit to an answering substation a signal indicative of the character of the call answered.

It is a further object of the invention to provide for use in a telephone system of the manual type an operators cord circuit which is equipped for selective signaling over multiparty lines and is so arrangedl that in handling a reverting call between two substations associated with the same line a special signal is transmitted over the line which indicates to the answering party the character of the call answered.

It is another object of the invention-to provide an improved operators cord circuit of the character described, wherein provisions are made for automatically releasing the selective signal-ing equipmentwhen the answer plug of the circuit is withdrawn from a line jack.`

It is still another object of the invention to provide in a telephone system of the manual type an improved disconnect signaling network which is so arranged that the line disconnect signal of the operators cord circuit is onlyenergized when aconnecticn resulting from a call of the revertive type is released at both the calling andcalled substations.

It is a further object of the invention to provide improved apparatus of the character described, which is simple in arrangement, is positive and reliable in operation, and requires a minimum of circuit equipment.

The invention is illustrated in its embodiment in a system of the automatic type and also. in a system of the manual type, both systems being arranged to serve subscribers lines-of the multiparty type. In both systems, facilitiesare provided for selectively signaling the substations associated with the multiparty lines in setting up connections involving these lines, and each system includes, in accordance with the present invention, apparatus operative in response to the answering of a reverting call for indicating to the answering party that the answered call is of the revertive type. In the automatic system, this apparatus is included in a reverting call switch, which switch is accessible to certain of the selector or connector switches of the system and includes apparatus directively controllable over a connection routed thereto from a calling line of the system for impressing upon the calling line the one of a plurality of ringing voltages having the station indicating characteristic corresponding to a desired called substation served by the calling line. The reverting call switch further comprises a ring cut-off relay and a slow-to-operate control relay which are sequentially operative in the order named in response to the answering of a reverting call at one of the substations associated with the calling line. These relays function to terminate the ringing operation and to transmit a special signal of limited duration over the calling line for the purpose of informing the answering party that the answered call is of the revertive type.

In the disclosed embodiment of the manual system, the subscribers lines are terminated at line jacks provided at the operators switchboard in the usual manner. An operators cord circuit is provided at each operators position which is adapted for use in setting up connections between the subscribers lines and is equipped with facilities for selectively signaling the substations associated with the multiparty lines of the system. More specifically, each cord circuit comprises an answer plug'which is providedfwith a pair of line contacts and a control contact and is adapted t be inserted in the line jacks for the purpose of answering calls initiated on the subscribers lines. Each cord circuit has associated therewith a plurality of sources of ringing voltage having different station designating characteristics, and is equipped with a ringing voltage selecting switch. This switch has a normal setting and is selectively operable to any one of a plurality of offnormal settings to impress a selected one of the ringing voltages upon a calling multiparty subscribers line in handling a reverting call involving two of the substations served by the calling line. The cord circuit further includes apparatus operative in response to the answering of the call at one of the substations associated with the calling line for terminating the ringing operation and for transmitting a special signal of limited duration over the calling line to indicate to the answering party that the answered call is of the revertive type. Provisions are also made in the cord circuit whereby the ringing voltage selecting switch is automatically restored to normal in response to removal of the answer plug from the jack terminating the calling multiparty subscribers line. For the purpose of informing the operator when a reverting call connection established between two substations served by the same line is released, a disconnect signal device is provided which is so controlled that it is only energized in response to the release of the connection at both the calling and the called substations.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figures l and 2, when placed end to end in the order named, illustrate an automatic telephone system having embodied therein the features of the invention briefly outlined above, and Fig. 3 illustrates a telephone system of the manual type, also having embodied therein the features of the invention briey referred to above.

Referring now more particularly to Figs. l and 2 of the drawings, the telephone system there illustrated comprises an exchange at which are terminated a plurality of subscribers lines, including the lines IIJ and I I. The exchange comprises a plurality of finder-connector links, including the link I5, for setting up connections between the various subscribers lines. For the purpose of assigning idle ones of the finder-connector links to the use of calling lines in a predetermined order, a distributor 30 is provided. This distributor is arranged to be controlled over a start circuit commonly extending to the various line circuits at; which the subscribers lines are individually terminated, the two illustrated lines I0 and II being shown as extending to the line circuits Illa and IIa, respectively. Certain of the subscribers lines are of the multiparty type, each having associated therewith two or more substations. Thus, the subscribers line I0 is illustrated as being connected to provide service to the two substations A and B. The line II, on the other hand, extends only to the substation C. For the purpose of selectively signaling the substations associated with the multiparty subscribers lines of the system in setting up reverting call connections, there are provided a plurality of reverting call switches, one of which is indicated generally at 35 as being accessible to the connector switch over a trunk line I2. The switching equipment of the exchange has associated therewith power and supervisory apparatus which includes a ringing current generator 40 and a ringinginterrupter 45. This apparatus may be of any desired construction and arrangement, it

being pointed out that the ringing interrupter 45 is arranged to impress the voltage of the ringing current generator 40 upon the five ringing current leads for coded intervals which are different in each instance. Thus, differently coded ringing voltages are provided for the selective signaling of the substations served by the multiparty lines of the system.

Each of the links provided in the exchange may be identical with the link I5, which is illustrated as comprising a finder portion or switch 20 and arconnector portion or switch 25, each having access to each subscribers line of the system. The finder switch and the connector switch included in each link may be of any conventional type, although preferably these switches are of the well-known Strowger type including two-motion switches forrperforming the line selecting functions. The connector portion of each link comprises impulse-responsive apparatus of any desined type for projecting ringing current of a selected code over an idle called multiparty subscribers line after the line has been seized by the switching mechanism included in the link. More specifically, each connector switch is arranged for switching through operation on calls to the lines forming predetermined groups such, for example, as calls routed to the trunks, extending to the reverting call switches. Each connector switch is also equipped with a code selecting switch which is directively controllable from any calling substation operatively to associate one of the ve illustrated ringing leads with a selected side of a selected called line. The distributor 30 may be of any desired construction and arrangement, although preferably this control unit is of the preselective type such that an idle link is selected for assignment to the use of a calling line each time a previously selected link is rendered busy.

Each of the reverting call switches embodied in the system may be identical with the reverting call switch 35, which is illustrated in Fig. 2 of the drawings as comprising a minor switch 290 through operation of which ringing current of the code corresponding to a desired substation may be selected under the control of a calling subscriber. This switch is of the well-known minor type and includes two sets of contacts 29I and 292 of eleven points each, wipers 293 and 294 individually associated with the two contact sets, a motor magnet 285 for driving the wipers over the contacts of their associated contact sets,

a release magnet 206., and a set of off-normal springs 2&1 which are operative into engagement when the wipers 293 and .294 are moved off normal. The control equipment of the switch 35 comprises a lineA relay R220, a slow-acting hold relay R230, a slow-acting. pulse-responsive relay R240, a ringing controlrelay R2I0, anda relay R200 which is operative to hold the switch operated during ringing periods. The control equipment further comprises a line switching relay R250, a control relay R260, a slow-acting ring cut-off relay R210, and a slow-to-operate signal control relay R280.. The two last-mentioned relays are arranged to control a circuit, described hereinafter, for impressing the voltage of a special tone `current source 46 upon an established connection which extends by way of one of the nder-connector links to a calling one of the subscribers lines. The source 45 may, if desired, comprise an alternating current generator having a predetermined output frequency such that a distinct-ive tone is produced when the output voltage thereof is reproduced.

In the operation of the system, if a call intended for the substation C, for example, is initiated at the substation A, a calling loop circuit is established by way of the line I when the calling subscriber removes the receiver provided at the calling substation from, its associated supporting hook or cradle. is completed, the line circuit I0a operates in the usual manner to mark the calling line in the bank contacts of the finder switches having access thereto, .and to impress starting ground potential upon the start lead CI3 extending to the link distributor 30. When this lead is grounded, the finder switch of the previouslyv assigned link operates` in a well-known man-ner to seize the calling line. Assuming that the nderconnector link I5 is utilized in setting up the connection, the wipers of the finder switch are first elevated to a marked position opposite the level of bank contacts terminating the group of ten lines and including ythe calling line I0, following which they are automatically rotated to a position into engagement with the contacts terminating the conductors of this line. When the calling line I0 is th-us seized, the `calling loop circuit is extended to the connector portion of the link, ground potential is impressed upon the private conductor of the calling line for the purpose of guarding this line against seizure, and the cut-oi relay conventionally embodied in the line circuit Illa is energized and operates to disconnect the start lead C.I3 from ground. In addition, Ithe line and hold relays embodied in the connector portion of the link operate to complete a marking path whereby the link is identified as busy in the link distributor 30. These relays, in operating, also function to impress ground potential upon the ringing apparatus start lead CM, thereby to initiate operation of the ringing current generator 4-0 and the ring-ing interrupter 45. These relays also operate to complete a circuit for transmitting the usual dial tone signal over the calling end of lthe connection, thereby to inform. the calling subscriber that the dialing operation may be started. The first two digits dialed at the calling substation are utilized for the purpose of selecting the desired line Il. More speciiically, when the iirst digit of the directory number 4designating the substation C is dialed, the wipers of the connector switch 25 are elevated to a position .opposite the level of bank contacts terminating the group When this loop circuit o ten lines including the called line II. The control relays of. the also operate to terminate the dial tone signal when the first digit is dialed at the calling substation. When the second digit of the directory 'num-ber designating the desired substation C is dialed, the wipers of the connector switch are rotated step by step at the rate of one step for each impulse so that at the end of the digitthey are left standing in engagement with the contacts terminating the conductors of the called line. Since the system is equipped for selective code ringing, a third digit must be dialed at the calling substation in order to condition the ringing control equipment embodied in the connector switch 25 for operation. At the end of this digit, the called line II is tested in the usual manner for the purpose of determining the idle or busy condition thereof. If the line II tests busy, the usual busy .tone signal is transmitted to the calling substation to inform the calling subscriber that the desired connection cannot immediately be obtained. In this case, no further operation of the switching apparatus occurs until the callis abandoned at the calling substation. The link I5 and the line circuit I0a are released in the usual manner when the calling subscriber replaces the receiver provided at the calling substation upon its supporting hook or cradle. If the called line II tests idle, the control equipment embodied in the connector switch 25 operates in the usual manner to impress ringing voltage of the selected code upon the line II, thereby to energize the ringer provided at the called substation C. This equipment also operates to transmit ringing current over the calling end of the connection to inform the calling subscriber that the called substation is being rung. The desired conversational circuit between the two substations A and C is completed when the call is answered at the called substation. More particularly, when the receiver provided at the called substation is removed from its supporting hook or cradle, a loop circuit is completed by way of the line II for energizing the ring cut-01T relay conventionally embodied in the connector switch 25. This relay, in operating, opens the ringing current circuits and completes a vtalking circuit which extends through the link I5 and connects the calling line I0 with the called line II.

Preferably, the arrangement of the control appanatus embodied in the connector switch 25 is such that the release of the connection is entirely under the control of the calling subscriber. As thus connected, when the calling party replaces the receiver provided at the calling substation A upon its supporting hook or cradle to interrupt the loop circuit extending to the connector switch 25, this switch, the iinder switch 2G, and the line circuits Illa and l Ia are released in a conventional manner well understood in the art.

In the event the above-described call originating at the substation A and routed to the finderconnector link I5, is intended for the substation B, also associated with the calling line I6, the calling party, after initiating the call, dials a rst digit .designating the group of trunks extending to the reverting call switches, and then the last digit of the directory number designating the substation B. The connector switch 25 responds to the impulses of the first digit by elevating its wipers to a position opposite the level of bank contacts terminating the group of trunks, including the trunk I2, extending to the reverting call switches. During the inter-digit pause between the rst and second digits, the connector switch 25 operates in the manner of a trunk-hunting selector to select an idle one of the reverting call switches. Assuming that the reverting call switch 35 is the first available idle switch of the group, the connector switch 25, upon positioning its wipers upon the contacts terminating the conductors of the trunk l2, arrests its operation and extends the calling loop circuit over the trunk |2 to the switch 35. When this occurs, the line relay R220 is energized over the calling loop circuit and operates to complete, at its contacts 22|, an obvious circuit for energizing the slow-acting hold relay R230. At its contacts 222, the relay R220 opens a point in the pulsing circuit, traced hereinafter, for energizing the slow-acting relay R240 in parallel with the motor magnet 295. The hold relay R230, in operating, opens, at its contacts 23| a vpoint in the marking path including the resistor 236 over which negative battery potential is normally impressed upon the private conductor |2c of the trunk I2 to indicate an idle condition of the switch 35. At its contacts 232, the relay R230 completes an obvious path for impressing ground potential upon the private conductor I 2c. When this conductor is connected to ground, locking circuits are completed for certain of the relays embodied in the connector switch 25, whereby this connector switch, the preceding finder switch 20, and the line circuit |a are pirevented from releasing. 'Ihe application of ground potential to the conductor |2c further serves to mark the reverting call switch 35 as busy in the bank contacts of the other connector switches. At its contacts 233, the relay R235, in operating, prepares a locking circuit for the ring cut-01T re=- lay R210. At its contacts 234, the relay R230 prepares the abovementioned circuit for transmitting current pulses to the magnet 295 and the relay R240 in parallel. At its contacts 235, the relay R230 opens a point in the operating circuit for the release magnet 296. Following the operation of the hold relay R230, the reverting call switch 35 is conditioned to respond to the impulses of the last digit of the directory number designating the desired substation B.

The line relay R220 follows the impulses of the second and nal digit dialed at the calling substation A and functions to repeat these impulses to the operating magnet 295 in parallel with the relay R240, whereby the wipers of the ringing code selecting switch 290 are operated into engagement with the set of contacts corresponding to the ringing code assigned to the substation B and the side of the line over which ringing current must be projected in order to energize the signal device provided at the called substation. More specifically, when the relay R220 restores at the beginning of the open circuit period of the irst impulse of the second digit, the above-mentioned circuit for energizing the relay R240 and the magnet 295, is completed. This circuit eX- tends from ground by way of the contacts 222, 234 and 203, and the respective windings of the magnet 295 and the relay R240 in parallel to battery. When initially energized over this circuit the relay R240 operates to open, at its contacts 24|, la point in the operated circuit for the relay R250. At its contacts 242, the relay R240 opens a point in the operating circuit for the line switching relay R250. The magnet 295 also operates when energized over the above-traced cir-- cuit, `and in cooperation with its associated ratchet and pawl mechanism, not shown, functions to advance the wipers 293 and 294 from their respective normal positions, illustrated in the drawings, into engagement with their respective associated first contacts. When these wipers are, moved off normal, the oil-normal springs 291 are operated into engagement to prepare the operating circuit for the relay R260.

As indicated above, the number of impulses in the final digit of the directory number designating the desired substation B depends upon the particular code assigned to this substation, and also upon the side of the line l0 to which the ringer provided at this substation is connected. Thus, if the ringer provided at the substation B is bridged across the line conductors |0a and |00 in series with a condenser, and the code of the ringing current designating the substation B is the code 3, the wipers of the switch 290 may be operated to engage either their iifth or sixth contacts, and the ringer provided at the substation B will be energized during the ringing intervals. On the other hand, if the ringer provided at the substation B is connected in series with a condenser between the negative line conductor |9a' and ground, a final digit comprising Ve impulses must be dialed at the calling substation so that, at the end of the digit, the operating circuit for the line switching relay R250 is prepared. Finally, if the ringer provided at the substation B is connected in series with a condenser between the positive line conductor |0b and ground, a final digit comprising six impulses must be dialed at the calling substation.

Assuming that the ringer provided at the called substation is connected in the second manner described above, the line relay R220 operates and restores five times in response to the dialing of the digit 5 at the calling substation. Thus, five impulses are transmitted to the relay R240 in parallel with the operating magnet 295. Each time the line relay restores it opens the operat-- ing circuit for the hold relay R230 at its contacts 22|. Due to the slow-to-release characteristics of the relays R230 and R240, these relays remain operated during impulsing. It will be apparent that at the end of the iifth impulse the wipers of the switch 290 are left standing in engagement with their respective associated fifth contacts so that the third ringing code is selected. Shortly following the end of the digit, and with the line relay R220 in its operated position, the slow-acting relay R240 releases to complete the prepared operating circuits for the two relays R250 and R260. The operating circuit for the relay R250 extends from ground by way of the multipled odd-numbered contacts of the contact set 29|, the wiper 293, the contacts 242, and the winding of R250 to battery. When energized over this circuit the relay R250 operates and locks to ground through the contacts 255 and the off-normal springs 291. At its contacts 25| to 254, inclusive, the relay R250 rearranges the ringing circuits for the transmission of ringing current over the negative side of the calling line I0. The operating circuit for the relay R260 extends from ground by way of the off-normal springs 291, the. contacts 24| and the winding of R260 to battery. When thus energized, the relay R260 operates and locks to ground through th'e contacts 26| and the off-normal springs 291. At its contacts 263, the relay R260 opens the above-traced circuit for energizing the magnet 295 and the relay R240 in parallel. At its contacts 262, the relay R260 prepares an operating circuit for the relay R200.

vlead C40 at its contacts 216,

.After dialing the two digits of the reverting call directory number designating the substation B, the calling party at .the .substation A restores the receiver provided at .this substation to its rsupporting hook or cradle, thereby to interrupt the loop circuit .extending through the operated lnder-connector link l to vthe reverting call switch 35. When this loop circuit is interrupted, the line .relay .R220 is deenergized and restores to open, at its contacts ,22 I the .operating circuit for .the hold relay R230. At its contacts 222, the relay R220 completes the prepared operating circuit for the relay R200, this circuit extending from ground by way of the contacts 222, 234, 262 and 215, and the winding of R200 to battery. When thus energized, the relay R200 operates .to complete, at its contacts d, a multiple circuit for impressing ground potential upon the ringing apparatus start leadClil., thereby to maintain the operation of the ringing current Agenerator and fthe ringing interrupter 45. At

its contacts 203 (the .relay R200 prepares a circuit for energizing the start ringing relay R210 when the ringing interrupter 45 next operates to impress a groundpulse upon the picknup pulse lead C46. At its contacts 202, the relay R200 prepared a holding circuit for the relay R210. At its -contacts 20|, the relay R200 completes an obvious holding circuit for the slow-acting hold relay R230.

As indicated above, the ringing interrupter t5 is, in accordance with conventional practice, arranged to impress a ground pulse upon the pick-up Apulse lead C46 at the beginning of each code cycle. The purpose of this arrangement is to vprevent a partial or mutilated code from being transmitted over a selected called line. Following the voperation of the relay R200, and when the ringing interrupter next operates to `ground the lead C46, the relay R210 is energized over a circuit including this lead, the contacts 203 and the contacts 216. When thus energized, the relay R21-0 operates and locks to ground through the contacts 215 and 202. After this locking circuit is completed, the relay R210 disconnects multiple ground from the pick-up At its contacts 21| and 213, the relay R210 opens .two points in the circuit for energizing the line relay R220. At its contacts 2-i2 and 214, the relay R210 ccmpletes the ringing current circuit and connects the positive trunk conductor 12b to ground. Following the operation'of the relay R210, ringing current is, during each ringing period of the selected ringing code, projected over the negative side of the calling line I0 to energize the ringer provided at the called substation. The path traversed by the ringing current may be partially traced as extending through the exchange battery and the ringing current generator 40, through the contacts of certain of the coding relays embodied in the interrupter 45 and by way of the code 3 ringing lead, the wiper 204, the upper winding of R210, the contacts y252 and 2.12, the conductor 12a, .the line conductor 10a', and the series-connected ringer and `condenser bridged between the conductor 10a .and ground at the substation .B to the grounded terminal of the exchange battery. In the event the ringer provided at the called substation B is bridged between the conductors of the line 10 in series with a condenser, the return path of the ringing current .extends .by way of the line conductor 10b, the trunk conductor ,1212, and the contacts 214 'and254 'to the ground- .operating .circuit for the relay R280.

ed terminal of the exchange battery. In order more fully to vexplain the operation of the reverting .call switch 3.5, itis pointed out that if a substation .having a ringer .bridged between the .positiveside of its associated line and ground is to be signaled through operation of this switch, an even-numbered inal digit is dialed at the calling .substation and hence the relay :R250 is .not energized .at the end of the digit. With this .relay in its :restored position, the path of the ringing current extends by way of a selected one of the `coole leads, the wiper 294, the upper winding of R210, the .contacts 253 and '214, and the trunk conductor 12b to .the positive rside of the calling line. :In this case also, a ground return path extending over the trunk conductor 12a Vand .through the contacts 212 and 251 is provided for completing the ringing current circuit in those instances where the ringer yprovided at thecalled substation is bridged across the conductors of the associated lin'e.

When the call is answered at one of the subvstations associated With the line l0, the control equipment embodied in the reverting call switch 35 operates to terminate the transmission of ringing current over the calling line and to transmit over this linea special signal vof .limited duration. Thus, if the call is answered .at the called substation B, for examplaa direct current bridge is connected ,betweenthe conductors `of the line 10 to complete the .operating circuit for the ring cutoi rela-yRZH'il. This .circuit Vmay take either ,of two forms `depending upon the position of the relay R250. With the relay R250 in its restored position, the operating circuit for the relay R210 may be traced as extending from the negative .terminal .of .the exchange 'battery by way of .the ringing .current .genera-tor 41,01the .contacts of certain of the coding relays embodied in .the interrupter .45. the .selected code .3 ringing lead, the wiper 2.9.4..:the Vupper winding of R210, the contacts 25,3 .and .21.11, the conductor 12b, 'the conductor 10b, lthe bridge across the conductors of the line .10 at the called substation, the conductor tiiaptheconductor 12a, andthe contacts 212;and .251;to ground. Alternatively, if the relay R250 is operated, .thecircuit for-,energizing the relay R210 extends .by away of :the code .3 ringing lead, the wiper 294,. .the ,upper kwinding of R210, the contacts 252 .and 212, theconductors 12a and 10a',

rthe bridge across the conductors of the vline 10 at the called substation, .the conductors 10b and 12b, and .the contacts :21.4 .and 254 .to the .grounded .terminal .of :the exchange battery. When eneru gized `overeither of the circuits traced above, the relay vR210 first .operates to complete a locking .circuit .for itself, this circuit extending from .ground by .wayof the contacts 233 and 214 and .the .lower winding v.of `R210 to battery. rAt its .contacts.213, .the relayiR210cornpletes an obvious At its con ,tacts A2,11, the relay R210 prepares a path for impressing the-voltage of the special tone current source 14.6 upon the connection extending to the .substation B. Atits contacts 215, the relay R210 opensthe .previously traced operating circuit for .therelay R200. The relay R200 now restores to open, at its contacts .204, rthe completed Ypath for .impressing ground potential upon the start con- .its contacts 201the relayiR200 opens the locking .circuit-for :the hold relay R230.

The relay R210 restores in response to the release of the relay R200, and, at its contacts 211 and 213, again vR210 interrupts the previously traced circuits for transmitting ringing current over the line 10 and two points in the previously traced operating circuits for the ring cut-off relay R210. When its windings are again connected across the trunk conductors 12a and 12b, the line relay R220 is again energized and operates to recomplete the operating circuit for the hold relay R230. Thus, the hold relay R230 is prevented from restoring. At its contacts 222, the relay R220, in reoperating, opens a further point in the operating circuit for the relay R200. When the relay R210 restores it also functions to complete the above-mentioned path for impressing the voltage of the tone current source 46 upon the established loop circuit extending to the called substation B. This path may be traced as extending from the ungrounded terminal of the source 46 by way of the condenser 203, the contacts 281, 211 and 213 tothe positive side of the connection extending to the substation B. The current traversing this path is transmitted through the windings of the receiver provided at the substation B, back over the negative side of the established connection and through the lower winding of the relay R220 to the grounded terminal of the source 40. The frequency of the current traversing this circuit is such that a distinctive tone is produced through operation of the receiver provided at the substation B. This tone serves to inform the answering party that the call which has been answered is a reverting call. Upon receiving this signal the answering party is informed that the answered call has not been abandoned, and further, that a short time interval may elapse before the calling subscriber again removes his receiver from its supporting hook or cradle to complete the desired connection. Shortly after the signaling circuit just traced is completed, the slow-to-operate relay R280, which is normally shunted by the condenser 204 in series with the exchange battery, operates. This relay, in operating, opens, at its contacts 281, the special signal circuit, whereby the signal is terminated. At its contacts 282, the relay R280 opens the path including the condenser 284 over which the exchange battery is normally connected in shunt with its winding, thereby to render itself fast to release.

As indicated above, the desired conversational circuit is completed when the calling subscriber at the substation A again removes the receiver provided at this substation from its supporting hook or cradle. With the arrangement illustrated, talking battery is supplied to the line 10 through the windings of the line relay R220, and the reverting call switch 35 is held operated until the connection is released at both the calling and called substations. More specifically, when the receivers respectively provided at the substations A and B are restored to their respective supporting hooks or cradles, the calling loop circuit is interrupted to cause the deenergization and release of the line relay R220. This relay, in releasing, opens, at its contacts 22|, the operating circuit for the hold relay R230. The relay R230, in releasing, disconnects the private or release conductor 12e from ground, thereby to cause 'the release of the connector switch 25, the finder switch 20, and the line circuit 10a. in the usual manner. At its contacts 231, the relay R230 connects the private conductor 12o throughthe re,.

sistor 236 to the negative terminal of the exchange battery, whereby the reverting call switch vis marked as idle in the bank contacts of the various connector switches. At its contacts 233, the relay R230 opens the previously traced locking circuit for the relay R210. At its contacts 235 the relay R230 completes a circuit extending through the contacts 264, for energizing the release magnet 206. When this magnet is energized, the wipers 293 and 204 are returned to their respective normal positions in the usual manner. When the switch 290 is thus normalized, the offnormal springs 291 are moved out of engagement to deenergize the relays R250 and R250. The relay R210, in restoring, opens the operating circuit for the relay R280, and a further point in thespecial signaling circuit traced above. Thus,

- the reverting call switch 35 is fully released.

From the above explanation it will be understood that the ringers respectively provided at the calling and called substations associated with the same multiparty line may, in certain instances, be arranged for energization over different sides of the line. Accordingly, the ringer provided at the calling substation is not energized during the ringing operation and the calling subscriber is not signaled as to when the call is answered. In such case the calling subscriber, after hanging up to initiate the ringing operation in the manner just described, waits a reasonable time interval and then picks up his receiver to again establish a connection with the line. If during this interval the call is answered at the called substation, the special signal transmitted to this substation serves to inform the answering party that the call is of the reverting type. On the other hand, if the subscriber at the calling substation removes the receiver provided at this substation from its supporting hook or cradle before the call is answered,'the current transmitted through the receiver provided at this substation from the tone current source 43 serves to signal the calling subscriber that the call has not been answered. In such case the calling subscriber may either abandon the call to cause the release of the equipment in the manner explained above, or may hold the connection until the call is answered.

Referring now more particularly to Fig. 3 of the drawings, the system there illustrated comprises a plurality of subscribers lines which are terminated in line jacks at the operators switchboard of a manual exchange. Thus, the subscribers line 50 is illustrated as extending to a line jack 313 which is provided at one of the operators positions of an operators switchboard in the manual office. The line jack 313 forms a part of a line circuit 55 which also includes the line relay R300, the sleeve relay R310 and the line signal lamp 302. Certain of the lines terrni nating at the operators switchboard are of the multiparty type. Thus, the line 50 is illustrated as serving the two substations D and E. For the purpose of setting up connections between the various subscribers lines of the system, each operators position at the switchboard is equipped with an operators cord circuit. Thus, at the position wherein the line jack 313 is located, there is provided an operators cord circuit 60 which is illustrated as comprising an answer plug 322, an operators telephone set 328, an answer key 321, a pair of ringing control keys 342 and 365,

cuit further comprises a ringing code selecting switch 350 of the Well-known minor type. This switch includes a single set of contacts 33| of eleven points, a wiper 352, an operating magnet 353 for driving the wiper 352 over its associated contacts, a release magnet 354, and a pair of offnormal springs 365. The contacts of this switch terminate ten ringing leads which are arranged to be connected to the high potential terminal of a ringing current generator 'I3 through operation of a cyclically operating ringing interruptor 65. This interrupter may be of any desired arrangement and functions to impress the voltage of the ringing current generator 19 upon the ten code leads for diiferently coded rperiods of each ringing cycle. Provisions are also made in the ringing interrupter 35 for impressing a ground pulse on the pickup lead C311 at the beginning of each ringing cycle. For the purpose of directively controlling the code selecting switch 35i] to select any one of the ten ringing leads terminating in the contacts thereof, there is provided a calling device 380, which is arranged to be connected in circuit with the operating magnet 363 over a circuit controlled by the key 315. For the purpose of transmitting a special signal over calling ones of the multiparty lines in setting up reverting call connections, there is further provided in association with the operators cord circuits, a special tone current source 353. source may, for example, comprise an alternating current generator having a predetermined output frequency within the audio range.

Referring now more particularly to the operation of the apparatus, illustrated in Fig. 3 of the drawings, to set up a reverting call connection between two substations associated with the same line, it may be assumed that a call intended for the substation D is initiated at the substation E, and, further, that the line 53 serving these substations is arranged for bridged ringing. When the call is initiated at the substation E, a loop circuit including the winding of the line relay R303 is completed in the usual manner. This relay, in operating, completes, at its contacts 33|, an obvious circuit for energizing the line signal lamp 352. The operator attending the position at which the jack 3|3 is terminated, upon observing the lighted condition of the lamp 302, is informed that a call is present on the line 53 which should be answered. To answer the call, the operator inserts the answer plug 322 in the jack 3|3. In response to this operation the line conductors 53a and 53h are connected through the tip and ring contacts of the jack 3 |13 and the plug 322 to the line conductors of the operators cord circuit. In addition, a circuit is completed at the sleeve contacts 325 and 3|3 for energizing the cut-oif relay R3|3 in series with the release relay R323. The relay vR3||), in operating, opens its contacts 3|| and 3|2, thereby to disconnect the windings of the line relay R330 from the condoctors of the line 53. The operating circuit for the relay R333 is thus broken, and this relay restores to open its contacts 33|, thereby to deenergize the signal lamp 332. The relay R323 in operating, opens a point in the circuit for energizing the release magnet 364. After inserting the plug 322 in the jack 3|3, the operator may actuate the key 321 to its off-normal position in order to connect the telephone set 323 to the line 55 and thus establish a talking circuit with the calling substation E. After this circuit is established, the operator may converse with the calling subscriber and ascertain the This party desired. Upon ascertaining that the substation D is desired by the calling subscriber, the operator may operate the key 342 to its off-normal position for the purpose of interrupting the ringing current circuit, operate the key 315 to its olf-normal position to prepare the operating circuit or the magnet 353, and actuate the calling device 33|) to the position corresponding to the code designating the desired substation D. When the key 315 is operated to its off-normal position a circuit including the contacts 315a and the pulsing springs 33M is completed for energizing the relay R335. This relay, in operating, opens a point in the circuit for energizing the magnet 353. Assuming that the fifth ringing code is assigned to the substation D, the operator dials the digit 5 to transmit iive current pulses through the engaged contacts of the key 315 and the winding of the magnet 353. Thus, when the dial of the calling device is moved off-normal, the oiilnormal springs 383D are closed to complete an obvious operating circuit for the relay R333. The relay R395, in operating, prepares the circuit for energizing the magnet 363. During the return movement of the dial ve current pulses are transmitted by the relay R385 to the magnet 333 over a circuit including the contacts 335 and 33|, and the contacts 315D of the key 315. When the dial cf the calling device is returned to its normal position, the onf-normal springs 333i) are disengaged to deenergize the relay R390. This relay, in releasing, opens, at its contacts 33|, a further point in the operating circuit for the magnet 353. Each time the magnet 353 is Y energized, it cooperates with its associated ratchet and pawl mechanism to advance the wiper 352 one step so that at the conclusion of the digit this wiper is left standing in engagement with the contact terminating the code 5 ringing lead. When the Wiper 352 is moved oil normal, the off-normal springs 335 are operated into engagement to prepare a circuit for energizing the release magnet 334. After the ringing code is thus selected, the operator may open the circuit for energizing the magnet 353 and deenergize the relay R335 by restoring the key 315 to its normal position. Following this operation, and in -order to initiate the ringing operation, the operator may restore the key i342 to normal and operate the key 335 to its-oi-normal position. After the key 355 is operated to its off-normal position, a ground pulse is transmitted over the pickup pulse lead C311 and through the springs 355b'and the contacts 31| to energize the start relay R313 at the beginning of the next cycle of operation of the coding relays embodied in the ringing interrupter 55. When thus energized the relay R315 operates and locks to ground through the contacts 312 and the switch springs 365a. After this locking circuit is completed, the relay R313 opens its operating circuit and disconnects ground from the pickup lead C311 at its contacts 31|. At its contacts 313, the relay R313 completes the circuit for transmitting ringing current of the code 5 over the calling line 53 to energize the signal device provided at the called substation D. The circuit traversed by this current extends from one terminal of the ringing current generator 10 through the contacts of the coding relays embodied in the interruptor 65 and by way of the code 5 ringing lead, the wiper 332, the lower winding of R330, the contacts 313, i334 and 344, the contacts 324 and 3I5, the line conductor 53h, the ringer and condenser bridged across the conductors of the line 50 at the called substation D, the conductor 50a, the contacts 3|4 and 323, the switch springs 343, the contacts 332 and the exchange battery to the other terminal of the ringing current source. A portion `of this ringing current is also directed through the ringers respectively provided at the other substations associated with the line 50. The coded character of the signals produced by this current indicates, however, that the call is intended for the substation D.

When the call is answered at the called substation D, a direct current bridge is connected between the conductors of the line 50 to complete a circuit for energizing the ring cut-off relay R330. This circuit extends from theY negative terminal of the exchange battery through the ringing current generator and by way of certain of the contacts of the code interrupter relays, the code 5 ringing lead, the wiper 362, the lower winding of R330, the contacts 313, 334, 344, 324 and 3|5, the conductor 50h, the direct current bridge across the conductors of the line 50, the conductor 50a and the contacts 3|4, 323, 343 and 332 to the grounded terminal of the exchange battery. When thus energized the relay R330 first operates to complete a locking circuit for itself, this locking circuit extending from ground through the lower winding of R3|0 and by way of the contacts 3|6, 325 and 336, and the upper winding of R330 to battery. After this circuit is L completed, the relay R330 completes its operation to open, at its contacts 332 and '334, two points in the above-traced ringing circuit and two points in its own operating circuit. At its contacts 333 and' 335, the relay R330 bridges the windings of the combined battery feed and supervisory relay R340 across the conductors of the line 50. At its contacts 331, the relay R330 completes an obvious circuit for energizing the slow-to-release relay R350. At its contacts 33|, the relay R330 completes the previously mentioned circuitl for impressing the voltage of the special tone current source 353 upon the loop circuit extending to the called substation D. More specically, current derived from the source 353 is transmitted over f the line 50 to energize the receiver provided at the substation D over a circuit which includes the condenser 338, the contacts 33|, 352, 333, 343, 323 and 3|4, the conductor 50a, the receiver provided at the substation D, the conductor 50h, the contacts 3|5, 324, 344 and 335, the lower winding of R340, and the exchange battery to the grounded terminal of the source I353. This current, as reproduced by the receiver provided at the substation D, serves to inform the party answering the call at the substation D that the answered call is of the revertive type.

When its windings are bridged across the conductors of the line 50 in the manner explained above, the relay R340 is energized over the loop circuit including this line, and operates to open, at its contacts 34|, a point in the circuit for energizing the supervisory lamp 354. Shortly following the operation of the relay R330, the slowto-operate control relay R350 operates to open,

calling and called substations is completed when the calling party at the substation E again removes the receiver provided at Lthis substation from its supporting hook or cradle, thereby operatively to associate the telephone set in use at this substation with the line 50. In this regard it will be apparent that when the lines are arranged for bridged ringing, the calling party is informed that the call is answered when the ringing operation is arrested. After the connection is fully completed, in the manner J'ust described, talking battery is supplied to the transmitters provided at the calling and called substations through the windings of the relay R340.

The release of the connection and of the operators cord circuit 60 is, of course, controlled by the operator attending the position at which this circuit is provided. More specically, when the call is cleared out at both the calling and called substations, the loop circuit extending by way of the line '50 and through the windings of the line relay R340 is interrupted. The relay R340 is thus deenergized and restores to complete, at its contacts 34|, the above-mentioned circuit for energizing the supervisory lamp 354, this circuit extending from ground by way of the contacts 35| and 34|, and the filament of the lamp 354 to battery. The resulting illumination of this lamp serves to inform the operator attending the position at which the cord circuit 60 is provided, that the connection is ready to be released. In order to release the connection, the operator restores the key 365 to its norma] position to open the operating and locking circuits for the relay R310, and withdraws the answer plug 322 from the line jack 3|3. In response to the last-mentioned operation, the previously traced circuits for energizing the cut-off relay R3|0 in series with the parallel-connected relays R320 and R330 are broken, causing all three of these relays to restore. The relay R330, in releasing, opens the operating circuit for the relay R350, causing the latter relay to restore and open the circuit for energizing the supervisory lamp 354. Thus, all of the illustrated relays of the operators cord circuit are restored to normal. The relay R320, in releasing, completes, at its contacts 32|, a circuit extending through the oir-normal springs 366 for energizing the release magnet 364. When this magnet is energized, the wiper 362 of the code selecting switch 360 is restored to normal position in the usual manner. Further, the release of this switch results in the disengagement of the off-normal springs 356 to deenergize the release magnet 364'. Following the release of the code selecting switch in the manner just explained, the operators cord circuit is fully restored to normal.

Although the arrangement illustrated in Fig. 3 of the drawings has been described with reference to the use of bridged ringing in signal- ,ing the substations associated with the multiparty lines of the system, it will be understood that by providing an arrangement similar to that incorporated in the reverting call switch 35 for selectively associating either'the tip contact or the ring contact of the answer plug 322 with the ringing lead extending to the wiper 362 of theV code selecting switch, the circuit may be adapted for use in signaling over multiparty lines arranged for divided ringing. It will also be understood that with the operators cord circuit 60 equipped to signal over lines arranged for divided ringing, the special signal transmitted over a line of this character in setting up a sponse to the answering of the .call at saidcalled substation -for arresting -thetransmission of ring- -reverting icall .-connection' will Vnot fonlyserve to signal an answering called party of the character of thecallanswere'd, .but in -each .instance where suchtacally is, in .feiect,; answered ,at the calling vsubstation, will serve; 'to ;.inform the .call- -ing subscriber Jthat'fthe call jhasfnotpreviously lbeen answeredatthe called substation. It will further vbe apparent that .theoperatolisi Cord circuit 60 mayinclude-.the .usualprovisons for setting up r connectionsv between .twozsub'stations associated with* different.rsubscrbersflines- In the interests of simplifyingfthe *.disclosure, .howeven the conventional portion .'o'f ..the cordjcircuit namely, 'that utilized 1' in establishing agtalking circuit between two :different lines, has been omitted.

WhileithereshaveA beengzdescribedwhat are at present consideredA to .be the preferred Y.embodiments ofthe invention,:itwill beunderstood that various modifications maysbe :made theren, and

it Vis intended c to .tcoverlin the f appended claims, all such modifications as .fall within;` the true spirit andlscope of the invention.

What' is` claimed@v is:

1. In a telephone system, a ;multip arty sub-4 scribers line, means foriselectively signaling; the substations f, associated with -said linein setting up revertingVv call connections between saidsubstations; yand means; comprising A:a1-relay' which vis energized over saidzlineiin response to the al1- swering of a 'reverting' call. at; one A`of; said substations for transmitting a 'signalftcthe :answering substation.

2. In a telephone f system, amultipartyzzsubscribers line, means for selectively signaling-the 'substations associate'df'with frsaid line iny setting up reverting' cali .connections '.between said substations;` and 'means .comprising a relay 'which is energized over saidtlinein response vto thevanswerin'g of a reverting `callrai-,rone of'said'substations for indicating .to the: `answering party that thek answered call -is a'rever.tingY call.

3.' In a telephonef-systemga .multiparty 'subscribers line, meansaforfselectivelyasignaling the substations associated with said lineV in-settingv,f45

up reverting calll connections between `said substations, and `means operative in` response -to the response to theY answering of a-vreverting 'call 1at one of said substations fortransmitting asignal to the answering substation, and means operative 'in responseA to operationosaid-last-namedmeans forterminating said signalaiter a: predetermined time interval.

5. In a 'telephone-system, a subscribers line, a pair of substations associated with'said'line, means 'for transmitting'ringing current to a called one of saidvsubstations in-settingiv upa connection between'said'substations, and nieanscomprising 1 'a relay which' isenergized 'over said'line in rem sponse to the answering ofthecall atsaid called substation for indicating to-.ithe Aanswering party that the'answer'ed call is fa-reverting call.

6. In av telephone system, ai subscribers line, a pair of substations associated with said line,

'means for transmittingringing current to aA called one of said substations insetting Yup a connection Abetween said.` substations; and means' comprising a relay which is fenergizedover saidrline `-1n reing current over said line and for `indicating to the answering party that-the answered call is a reverting call.

'7. In a telephone system, a ,subscribers line, a pair of substations associated with vsaid line, means for transmittingringing.currenttoa called one of said substations in setting up a connection 'between said substationsand means comprising a :relay which is energized over said .line in response to .a call answering .operatiomperformed at one of said substations for arrestingthe 4transmissioncf ringing currentover said line andfor impressing a `predetermined signal voltage upon said line.

8. In a telephone system, la subscribers-line, a pair of substationsassociated with-.said line, meanslfor .transmitting `ringing currentto .a called one vof said substations in setting up a connection between Y said substations, and means .operative in response to a call answering operation .performed at one ofsaid substations for arresting thertransmission of ringing current oversaid line and Yfor impressing apredetermined signal Avoltage upon'said line, wherebythe answering party is informed that the call'isa revertingicall if.' the call isvanswered at the called-substation .and is informed that the call has not beenfanswered at the called substation if tthe;call\ ar1swering operation is performed at thecalling substation.

9. Ina telephone system, `asubscribers line, @a pair of substations associated with said line, means for transmitting ringingcurrent to al Called 4one of saidfsubstationsin setting up a connection betweensaid substations,v meansoperative in response to acall answering operation performed at oneA of said substations for arresting the transmission of ringingcurrent over said lineand .for impressing a predetermined, signal :voltage .upon

vsaid linefandmeans operative inresponse .to opferation of said last-.named .means .for .removing saidsignal voltage from said-line -aftera predeterrnined time interval.

10. VIn an .automatietelephonesystem, a 4plurality of lines,-automaticswitching apparatusfor setting-up connections betweensaidlines and including means controllable over ra .calling multiparty linefor .impressing ringing-f-voltageon the calling line to signal a called substationassociated with the lcalling line,andgmeans `comprisinga relay which is energized .oversaid .line in responseto the answering of .thecall at one of the substations associated '.with. said callingline for transmitting a special signal to the answering substation.

l1. In an automatic telephone system.. al, plural- .ity of lines, automatic switching apparatus for calling line tosignala called vsubstatim associated with -thecalling line, meansoperativelin response -to the, answering/...of .y the .caf/ll. atfonebf the substations associated with said calling line for removing ringing voltage from said calling line and for impressing a. predetermined signal voltage upon said calling line, and means controlled by said last-named means for removing said signal voltage from said calling line after a predetermined time interval.

13. In an automatic telephonesystem, a plurality of lines including a multiparty subscribers line, ringing apparatus operative to provide ringing voltages `having diierent station indicating characteristics individually corresponding to the substations associated with said multiparty line, a reverting call switch, automatic switching apparatus for setting up connections between said lines and including a numerical switch directively controllable over said multiparty line from a calling substation associated therewith to route a connection to said reverting call switch, said reverting call switch being directively controllable over said connection from said calling substation to impress the ringing voltage corresponding to a called substation upon said multiparty line and including means operative in response to the answering of the call at a substation associated with said multiparty line for removing the ringing voltage from said multiparty line and for impressing a predetermined signal voltage upon said multiparty line.

14. In an automatic telephone system, a plurality of lines including a multiparty subscribers line, ringing apparatus operative to provide ringing voltages having different station indicating characteristics individually corresponding to the substations associated with said multiparty line, a reverting call switch, automatic switching apparatus for setting up connections between said lines and including a numerical switch directively controllable over said multiparty lline from a callingsubstation associated therewith to route a connection to said reverting call switch, said reverting call switch being directively controllable over said connection from said calling substation to impress the ringing voltage corresponding to a called substation upon said multiparty line and including means operative in response to the answering of the call at said called substation for transmitting a signal to the answering party indicating that the yanswered call is a reverting call.

-15. In an automatic telephone system, a plurality of lines including a multiparty subscribers line, ringing apparatus operative to provide ringing voltages having different station indicating characteristics individually corresponding to the substations associated with said multiparty line, a reverting call switch, automatic switching apparatus for setting up connections between said lines and including a numerical switch directively controllable over said multiparty line -from a calling substation associated therewith to route a connection to said reverting call switch, said reverting call switch being directively controllable over said connection from said calling substation to impress the ringing voltage corresponding to a called substation upon said multiparty line and including a ring cut-off relay and a slow-tc-operate control relay sequentially operative in the order named in response to the answering of the call at one of the substations associated with said multiparty line, and means controlled by said relays for removing the ringing voltage from said multiparty line and for transmitting a signal of limited duration over said multiparty 'line to the answering substation. v' l 16. In combination with a plurality of ringing voltage sources, a reverting call switch having a trunk extending thereto and comprising means directively controllable over said trunk for impressing a selected one of said voltages upon said trunk, and means comprising a relay which is controllable over said trunk after the selected ringing voltage has been impressed thereon for removing the selected rin-ging voltage from said trunk and for impressing a predetermined signal voltage upon said trunk.

17. In combination with a plurality of ringing voltage sources, a reverting call switch having a trunk extending thereto and comprising means directively controllable over said trunk for impressing a selected one of said voltages upon said trunk, and means controllable over said trunk for removing the selected ringing voltage from said trunk and for transmitting a signal of limited duration over said trunk.

18. In combination with a plurality of ringing voltage sources, a revertingv call switch having a trunk extending thereto and comprising means directively controllable over said trunk for impressing a selected one of saidvoltages upon said trunk, means controllable over said trunk for removingthe selected ringing voltage from said trunk and for 'impressing a predetermined signal voltage upon said trunk, and means operative in response to operation of said lastnamed means for removing said signal voltage from said trunk after a predetermined time interval.

19. In combination with a plurality of ringing voltage sources, a reverting call switch having a trunk extending thereto and comprising means directively controllable over said trunk for impressing the voltage of a selected one of said sources upon said trunk, a ring cut-off relay and a slow-to-operate control relay sequentially operative in response to the completion of a loop circuit including said trunk, and means controlled by said relays for removing the ringing voltage from said trunk and for transmitting a special signal of limited duration over said trunk.

20. In combination with a plurality of ringing voltage sources, a reverting call switch having a trunk extending thereto and comprising means directively controllable over a loop circuit including said trunk and operative in response to the interruption of said loop circuit for impressing the voltage of a selected one of said sources -upon said trunk, a ring cut-oil relay and a slowto-operate controly relay sequentially operative in response to the recompletion of said loop circuit, and means controlled by said relays for removing the ringing voltage from said trunk and for transmitting a special signal of limited duration over said trunk.

21. Ina telephone system, an operators switchboard, a multiparty subscribers line terminating at said switchboard, and an operators cord circuit including means for selectively signaling the substations associated with said line in setting up reverting call connections between said substations, and means comprising a relay which is energized over said line in response to the answering of a reverting call at one of said substations for transmitting a special signal to the answering substation. v

22. In a telephone system, an operators switchboard, a multiparty subscribers line terminat- 32,287,383 .ingat'x saidswitchboarmuandcan operatorsacord .ihoardg a5multipartypsubscribens lineaterminating circuiti including means .forx's'electively signaling Vithe.:sulcstations associated;withmsaid line in set- `ting vup reverting ,.call connectionsb'etween said substations,::m'eans operative lin lresponse to the answering vof :a reverting callfat oneof said* substations fortransmittinga special signal tothe `answering substation,` 'and meansvoperative in response tooperation of vsaid :la'st-:namedimeans for terminating saidsignalV after a predetermined .time interval.

23. Inra telephone system, a operatorsfswitch- "board, "af multiparty `subscriloers line Aterminating vatsaid switchboard, andan operators cord cirmeans'contrclledbysaid relays for transmitting a specialA signal of limited .duration over said .line toV the answeringsubstation.

24. In altelephone system, a rplurality of ringing` voltage sources having different .station indicating characteristics, an operator-s lswitchboard, a multipartysubscribers 'line terminating 'at aline jack provided atv said operators switchboard, and anv operators cord circuit 'including an answer plug adapted to be inserted into lsaid jaclctofanswer a call'initiated at one of thesubstations associated with said line, a ringing volt- `age selecting switch having va `normal setting vand-selectively operable to any one of-'a plurality I of oli-normal settings to impress a selected one of said. voltages Yupon said line in `settingup reverting callconnections between saidlsubstations, means operative in response to the answering of va reverting call latoneof v'said' substations for removing the selected' ringing voltage"'from"said Aline and for transmitting-'a specialfsignal Vtothe answering substation, and means operative in response to removal of ysaidfanswer plug -from said jack for normalizing said'sw'itch.

25. In a telephone'system, a plurality of ringing voltage sources hav-ing differentstation indicating characteristics, -an operators switchhoard, a multiparty subscribers line terminating at a line jack provided at said operatorsswitchboard, Aand an operators cord circuit including ananswer plug adaptedto be insertedinto said jack to answer a call initiated at one of the substations-associated with said line, an impulse responsive ringing voltage selecting switch^-havf-` inga normal setting andl operative to any one Vof a-plurality of oif-normalsettingsito impress ay selected oneof said voltages upon said -lin'e in response to impulses transmitted thereto, thereby" selectively tosignal Isaid substations inset ting -up reverting call connectionsV therebetween, said switch including a release ymagnet operative "to cause saidv switch to restore" to normal, means for transmitting impulses to saidswitch, means verting-call at one of said substations for removing the selected ringing voltage from said line and ior transmitting -a special signal over said line to the answering substation, and means operative in response to removal of said answer plug from said jack for energizing said release magnet.

Cil

operative in response to the-answering of a re-t` 26. In a telephone system, a plurality of ringing voltage sources having different station indicating characteristics, an operators switchat a line jack providedzat: said.operators switchboard, .and .tan;cperator.s .cord circuit including ainl answerplug-i adapted .toi 'be finsertedi into. said jackto answerlaixzall:initiated'zat: one'of' `the 'substations'V associated with: said line, '.an:-impulse responsiveringing 'Voltage Aselecting :switch hav- .f ing a: ,normali setting and operative: to'r any one vofla .plurality vof fori-normal settings'. tol impress a selected-:orient said'svoltages upon said. line in 'response `to impulsestransmitted thereto, thereby 'selectively to signalrsaid substations 'in' setting up reverting icall connections therebetween, said switch including a release magnet operative to cause saidswlitchto restore :to normal,

`means for transmitting impulses to saidl switch, means' operative .inv response to the answering of fa-reverting ca'lllat one of' saidA substations for Yremoving-'the selected.v ringingfvoltage from said 'line and -for transmittinga'special signal over said line-.to the answering substation, and means 4'comprising-a' relay controlled over a circuit including .one of the. contacts 'fsaid plug for `energizingl'said release -magnet in response to re- -moval o'fasaid plug fromsaid jack.

`27. Ina telephone system, a `plurality=of ringing voltage 'sources having differentstation iindicating characteristics, an operators switchrboard, `a' multipartyfsubscribers line terminating at a line jack provided at said operators switch- *boa-rd, -andr an` operators cord circuit `including "a plug adapted to be inserted into` vsaid jack' in handling callsinvolving the substations associ- Vated with said line,la'rin`ging voltage selecting switchhaving a normal setting and selectively 'operale 'to' anyone of' a plurality VVof *cH-normal settings toA impress allselected one vof'said voltages upon saidfline-,aand means operative in response ltoremovall of `said plug from saidV jack'for normalizing said switch.

28. Ina telephone-systenna plurality l'of ringing voltage sources having different station indicating characteristicsyan operators' switchboard, *a multiparty subscribers `line terminating at a line 'jack provided at said operators switchboard,l and,V an'operators cord circuit including a plug adapted to 'be inserted-into said jack in handling calls involving the substations associe5ated with said line, a ringing lvoltagev selecting switch having anormal setting and selectively 'operable toany one of a plurality of 'off-normal adapted. tosbe inserted'intoisaid jack in handling -callsf.-involvingthe vsubstationsr associated with -said line,v an' impulse lresponsiveringing voltage vselecting,.switch-shaving a -normal @setting and Voperativeto any -one yof a pluralityof off-normal settings to impress a selected one of said voltages upon said line in response to impulses transmitted thereto, said switch including a release magnet operative to cause said switch to restore to normal, means for transmitting impulses to said switch, and means operative in response to removal of said answer plug from said jack for energizing said release magnet.

30. In combination with a plurality of ringing voltage sources having different station indicating characteristics, an operators cord circuit including a line connect plug having a pair of line contacts and a control contact, a ringing voltage selecting switch having a normal setting and selectively operable to any one of a plurality of oir-normal settings to impress a selected one of said voltages upon said line contacts, and means controlled over a circuit including said control contact for automatically restoring said switch to normal.

3l. In combination with a plurality of ringing voltage sources having diierent station indicating characteristics, an operators cord circuit including a line connect plug having a pair of line contacts and a control contact, an impulse responsive ringing voltage selecting switch having a normal setting and operative to any one of a plurality of off-normal settings to impress a selected one of said voltages upon said line in response to impulses transmitted thereto, said switch including a release magnet operative to cause saidy switch to restore to normal, means for transmitting impulses to said switch, and means controlled over a circuit including said control contact for energizing said release magnet.

32. In combination with a plurality of ringing voltage sources having diierent station indicating characteristics, an operators cord circuit including a line connect plug having a pair of line contacts, means for selectively impressing said voltages upon said contacts, and means controlled over a circuit including said contacts for removing a selected one of said voltages from said contacts and for impressing a predetermined signal voltage upon said contacts.

33. In combination with a plurality of ringing voltage sources having different station indicating characteristics, an operators cord circuit including a line connect plug having a pair of line v contacts, means for selectively impressing said voltages upon said contacts, means comprising a ring cut-off relay and a slow-to-operate control relay sequentially operative in the order named and controlled over said contacts for removing a selected one of said voltages from said contacts and for impressing a predetermined signal voltage upon said contacts for a predetermined time interval, a battery feed relay including windings connected to said contacts in response to operation of said ring cut-off relay, a signal device, and a circuit controlled by said control relay and said battery feed relay for energizing said signal device only after a reverting call connection established through operation of said cord circuit is released.

34. In combination with a plurality of ringing voltage sources having different station indicating characteristics, an operators cord circuit including a line connect plug having a pair of line contacts and a control contact, a ringing voltage selecting switch having a normal setting and selectively operable to any one of a plurality of off-normal settings to impress a selected one of said voltages upon said line contacts, means controlled over a circuit including said line contacts for removing a selected'one of said voltages from said line contacts and for impressing a predetermined signal voltage upon said line contacts, and means comprising a relay controlled over a circuit including said control contact for automatically restoring said switch to normal.

35. In a telephone system, an operators switchboard, a multiparty subscribers line terminating at a line jack provided at said switchboard, and an operators cord circuit including an answer plug adapted to be inserted into said jack to answer a call initiated at one of the substations associated with said line, means for selectively signaling said substations in setting up reverting call connections between said substations, a signal device, and means controlled over said line for energizing said signal device only when a reverting call connection set up through operation of said cord circuit is released.

36. In a telephone system, a line, a plurality of substations associated with said line, means for transmitting ringing current over said line to a called one of said substations in setting up a connection between said substations, means for automatically arresting the transmission of ringing current over said line when the call is answered, and means for transmitting a distinctive signal to the answering party when the call is answered, whereby the answering' party is informed that the answered call is a reverting call if the call is answered at the called substation and is informed that the call has not been answered at the called substation if the call answering operation is performed at the calling substation.'

37. In a telephone system, a line, a plurality of substations associated with said line, means for transmitting ringing current over said line to a called one of said substations in setting up a connection between said substations, means for automatically arresting the transmission of ringing current over said line when the call is answered, means for transmitting a distinctive signal to the answering party when the call is answered, whereby the answering party is informed that the answered call is a reverting call if the call is answered at the called substation and is informed that the call has not been answered at the called substation if the call answering operation is performed at the calling substation, and means for automatically terminating said signal a predetermined time interval after the transmission of ringing current over said line is arrested.

38. In a telephone system, a multiparty subscriber line, means for selectively signaling the substations associated with said line in setting up reverting call connections between said substations, and means for transmitting a distinctive signal over said line to the party answering a revertingcall, whereby the answering party is informed that the Yanswered call is a reverting call if the call is answered at the called substation and is informed that the call has not been answered at the called substation if the call answering operation is performed at the calling substation.

CLARENCE ERNEST LOMAX. 

